1. Field of the Invention
This invention relates to powered woodworking machinery and attachments for electric routers.
2. Description of the Related Art
a. Overview
Consideration of the nature of one of the two basic woodworking processes will illuminate the significant contribution the present invention makes to the ancient and noble art of woodworking.
All woodworking involves only two principal operations and one specialized operation. The principal operations are: (1) removal of wood tissue and (2) joining of wood tissue members. While much tissue removal involves removal of "waste" tissue from a workpiece, some operations, such as shingle splitting, involve separation of one "good" piece of wood from another "good" one. Thus, while tissue "separation" might be more descriptive, even this is, however, removal of one bit of wood tissue from another. A few woodworking specialities, including cooperage, musical instrument construction, boatbuilding and chairmaking also involve bending wood tissue. In short, things made of wood are made by shaping hunks of tree trunk, by removing and sometimes by bending wood tissue, and by fastening the hunks together.
The vast majority of woodworking tools, like the present invention, perform solely the first operation, tissue removal. Examples include the ax, saw, chisel, froe, plane, scraper, knife and coated abrasives ("sandpaper"). All conventional tissue removal tools utilize one or more cutting edges, and control of the cutting edge or edges is necessary to achieve controlled tissue removal. (Laser tissue removal tools "cut" by burning wood tissue.) Interestingly, tool complexity is generally inversely proportional to the skill required successfully to use the tool. ("Skill" is used here to mean muscular and hand-to-eye coordination and is to be distinguished from the understanding required to identify tissue which should be removed and to determine how a tool must be manipulated in order to accomplish that removal.)
While highly regulated and predictable wood tissue removal is desirable in most woodworking, predictable and regulated tissue removal is relatively difficult utilizing most hand woodworking tools, including both unpowered ones (e.g., handsaws, chisels, hand planes) and powered ones (e.g., hand circular saws, portable electric drills, electric routers). Consequently, the desire to achieve greater control of tissue removal has been one of the two principal objectives of wood tissue removal tool development. The quest for control has largely been a story of guides, gauges, fences, stops, carriages, clamps and holders.
While the search for control has been important and continues, it has often been eclipsed by the more dramatic changes in wood tissue removal technology relating to power. All wood tissue removal tools must have a "motive" force or energy source to operate the tool and, most basically, overcome the chemical and mechanical intra- and inter-tissue bonds ultimately derived from solar energy through photosynthesis within the tree from which the wood tissue came.
Historically, virtually all early tools were human or "hand" powered, and many simple tools continue to be hand powered today. As other power sources have been developed or harnessed, they have been utilized to power woodworking tools, resulting, for instance, in animal, water, gasoline and electrically powered tools.
In short, all tissue removal woodworking tool development may be seen as the adaptation of power to and efforts to achieve regulation in tissue removal. Despite the constancy of these objectives through the millenia of historically recorded woodworking, tool evolution continues because of continuing evolution of the technologies, such as metallurgy, used in making woodworking tools, continuing evolution in the technologies for powering them and the interplay among these technologies.
For instance, at the end of the last century, the substantial cost of a high power source of rotary motion, such as a steam or gasoline engine or water mill, coupled with the relatively low cost of iron castings, led to the development and extensive use of line-shaft woodworking shops. In them an entire shop of enormous tools was powered by a single power source through a complex (and dangerous) series of shafts and belts. However, modern electric motors make it far less expensive to dedicate a separate motor to each tool than to transmit rotary mechanical power to every tool from a single source, and thereby render the line-shaft shop obsolete.
The line-shaft shop economy in investment in a single power source remains desirable, nevertheless, even when tools are powered by a directly mounted electric motor, if a single motor can be conveniently used for multiple tools or multiple tool function without significant degradation of tool operation. Such an electric motor has only recently become available, largely because of advances in hand controlled power tools. As noted above, however, such hand power tools utilize structures providing for relatively unregulated tissue removal.
Relatively small electric motors have long been used for electric hand drills, which evolved directly from hand powered drills in that an electric motor, rather than a hand powered mechanism, is used to rotate the drill bit. While moderately high-powered electric drills have long been available, they have generally provided high power at the expense of rotational speed.
A related electric hand tool which, like an electric hand drill, also has a chuck mounted on the end of a rotating shaft, is the electric router. It has no exact hand-powered analog because it uses a rotating bit to perform tasks accomplished by linear motion hand tools, such as the hand router ("old woman's tooth"), rabbit plane, molding plane and chisel. In most instances, the router bit must rotate at a speed far higher than that required for drilling. As electric routers have been called upon to remove larger amounts of wood tissue in more substantial cuts, higher-power models have been developed. Furthermore, the desire to begin a cut without lateral movement, by plunging the bit into a workpiece along its rotating axis, resulted in development of the plunge router. Finally, the recent availability of compact, lightweight electric plunge routers described in more detail below, which use high power universal (ac/dc) motors, has made possible the present invention. In light of the general background set forth above, the present invention can be recognized as a significant advance in the historic effort to achieve highly regulated, controlled and predictable wood tissue removal with a minimum of effort and skill.
b. Plunge Routers and Related Tools
As indicated above, high power, plunge electric routers have come into widespread use in woodworking in recent years. Typical of such machines are the Makita 3612BR and the Hitachi TR12 models of plunge routers. Both use universal (AC/DC) motors which draw approximately 14 amps at 110 volts, and both use closely similar plunge mechanisms. Virtually all electric routers utilize a base which is adjustable with respect to the router motor and chuck mounted on the end of the motor shaft. Thus, with the router off, the position of a router bit mounted in the chuck may be adjusted relative to the base and, consequently, relative to a workpiece against which the base bears. By contrast, the base on a plunge router is mounted on a spring-loaded mechanism to allow relatively significant movement of the base relative to the router bit while the tool is in operation. This is typically achieved by a configuration in which two sleeves mounted on or in the router motor housing travel on two tubes which are mounted on the router base perpendicular to the base and parallel to the motor axis. Springs within the tubes urge the base away from the router motor so that pressing down on handles attached to the motor case or housing and against the base causes the router bit to protrude through the center of the base and to plunge into a workpiece. A lever-actuated lock associated with one of the sleeves is typically used to lock that sleeve against its tube, thereby locking the base in place.
Plunge routers were initially used primarily to make "blind" cutouts by plunging the bit or cutter into the workpiece and then moving it laterally following a pattern, as, for instance, in forming countertop sink cutouts. The utility of the plunge router for making slot mortises by clamping a workpiece in a jig having two rails on which the router base travels between stops was described by Tage Frid in issue no. 30, September 1981, of Fine Woodworking magazine. This article also disclosed the utility of spiral end mills in mortising using a plunge router and contributed to expansion of the popularity of plunge routers.
Such plunge routers are now widely owned by individual woodworkers and small woodworking shops. The same woodworkers periodically need the ability to accomplish slot mortising, horizontal boring and overarm routing operations, but commercially available equipment dedicated to such operations is prohibitively expensive, particularly in view of the relatively modest need individuals and smallshop woodworking operations typically have for such equipment.
Such woodworkers often also need a router table, which is basically a horizontal work surface under which a conventional router may be mounted in order to utilize it as a shaper by moving a workpiece relative to the router bit rather than moving the router and bit relative to the workpiece. Inexpensive router tables are commercially available and may be readily fabricated. However, such tables are frequently inconvenient to use because adjustment of router bit position must be accomplished by adjusting the router on its base, which is difficult to do with the router mounted upside down underneath a router table.
Numerous previous tool configurations have been developed in order to achieve controlled relative movement between a woodcutting tool rotating at high speed and a workpiece. For instance, conventional drill presses accomplish vertical boring with a configuration in which a chuck holding a drill bit travels vertically in order to drive the rotating boring bit into a stationary workpiece. Conventional horizontal boring machines orient the boring bit axis horizontally, and some move the workpiece while others move the bit. However, conventional horizontal boring machines typically bore multiple holes by utilization of multiple bits or by repositioning the workpiece on the boring machine, and not by repositioning the workpiece utilizing controlled movement of a workpiece support relative to the boring bit.
Combined function machines have also previously been developed. For instance, a combination boring, mortising, tenoning and duplicating woodworking tool is described in U.S. Pat. No. 4,593,735 to John C. J. Wirth, Jr. The Wirth machine utilizes a conventional motor or a router as a power source with the shaft mounted horizontally, and a workpiece is mounted on a table which is movable along two orthogonal horizontal axes. The cutting tool is movable in a vertical plane on a parallelogram, together with a follower to follow a pattern, thereby operating somewhat like a pantograph.
An apparatus for cutting dovetail joints is described in U.S. Pat. No. 4,163,465 to Strong. That apparatus comprises generally a vertical mounting plate intended to receive the base of a conventional router, which mounting plate travels vertically relative to a horizontal base. Thus a rotating woodcutting bit mounted above the base in the router may be moved up and down relative to the base to permit repositioning of the bit in order to make successive cuts in a workpiece which is slid along the base against a fence.
A horizontal boring capability is sometimes added to a conventional table saw by mounting a movable table on the side of the saw base adjacent to one end of the saw shaft. A chuck on that shaft receives boring and drill bits. While slot mortising may also be possible in principle using such a configuration, saw motor shafts typically rotate at approximately 3600 revolutions per minute, which is far slower than the appropriate speed for optimal mortising bit or end mill operation in wood.
None of these prior devices succeeds, however, in providing an economical, highly accurate and easily used apparatus for accomplishing horizonal boring, slot mortising, overarm routing and router table/shaping operations.